Retreating blade
The blade on a helicopter rotor whose tip is moving in the direction opposite to that in which the helicopter is moving.
Aviation Maintenance Technician Handbook — Airframe, p. G-29
Also defined in 1 more source
Any blade, located in a semicircular part of the rotor disk, in which the blade direction is opposite to the direction of flight.
Taught in AF-N Concepts, AF-N Quick reference.